The field of the invention relates generally to methods for recycling fibers. In particular, the field of the invention relates to a system and method for providing structurally reconstituted fibers from surplus fabric material such as cotton denim, wherein the fibers are opened, cleaned and structurally engineered for delivery to a card without defects such as fiber bundles (neps) or unopened threads. The reconstituted fibers are then used without binders to produce a finished nonwoven material having structural properties enabling it to be cross lapped and laminated, and exhibiting greater uniformity, strength, and higher absorption characteristics than was previously possible.
Increasing expenses associated with obtaining raw materials and constantly increasing consumption of textile products provide a strong economic incentive for developing methods for recycling surplus or unused textile material which would otherwise go to waste to be burned or buried. Large amounts of cloth scrap, clippings, and loose sample scraps are created at xe2x80x9ccut and sewxe2x80x9d plants where garments are manufactured. These scraps are waste material that comprise approximately 15-30% of all types of fabric manufactured for use in garments. Unless recycled into insulating materials or nonwoven matting, these cloth scraps and clippings become waste and are sent to landfills. Presently over 200 million pounds of cotton denim scrap material are burned or buried in landfills annually. Such reclaimed fibers are of importance in providing a foundational material for nonwoven fabric technologies that can be designed to replace traditional woven textiles.
In the past, surplus or recycled denim material was rejected as a base for producing fibers for a finished nonwoven product. Cotton denim is one of the toughest fabrics produced and is typically woven so tightly that its fibers cannot adequately be opened or regenerated for reuse. Conventional recycling methods cannot open surplus denim fibers sufficiently for reuse in a hydroentangled product. Conventional methods leave so many unopened threads and neps that a web containing such unopened fibers would be unsuitable for hydroentanglement. Conventional processes for opening denim result in fibers which are too short for hydroentanglement. Such fibers could only be used in conjunction with binders for rough material such as carpet underlayment.
New fabric formation techniques and advanced finishing processes are being used to accomplish fiber to fabric manipulation to provide a final product comprising nonwoven material. One method for producing a nonwoven material is accomplished by hydroentangling or spunlacing a fiber web. Conventional methods of fiber processing form the fiber web, which can be dry laid or wet laid after which the fibers are hydroentangled by means of a plurality of fine water jets under high pressure.
Conventional methods of recycling cloth scraps involve the use of high percentages of virgin (non-waste) carrier fibers or non-biodegradable synthetic fibers. Such conventional methods are inefficient and produce low quality yarn and consequently low quality fabrics. When high percentages (typically more than 50%) of virgin fibers are used, raw material costs are substantially higher and the amount of cloth/fibers recycled is low because the resulting yarn/fabric is primarily virgin/fabric.
Also, the yarn/fabric produced usually must be dyed to a required color since the large amount of carrier fibers required dilutes the color of the scrap material being recycled. This problem is of particular importance when recycling denim because it must be over coat dyed with indigo, the only accepted organic natural dye. Because most of the cloth scraps being recycled already have been dyed, it would be desirable to provide a recycling process which is capable of using a high percentage of dyed fibers in the raw material mix. Products derived from such recycled, dyed fibers or yarns would not require any additional dyeing. This advantageously would eliminate the many costs associated with dyeing yarns and fabrics.
Although non-biodegradable synthetic fibers are available, their use implicates serious environmental as well as cost concerns. The synthetic fibers lack the ability to retain dyes as efficiently as natural fibers, and they do not bond well with other fibers because of their slick surfaces. Furthermore, the resulting fabrics do not have the texture, quality, or acceptance level of premium natural fibers.
Therefore, what is needed is a method of recycling natural or synthetic fibers which can be needle punched and/or provided for hydroentanglement to produce a superior finished nonwoven product. What is also needed is a new method to effectively and efficiently recycle cloth scraps into substantially virgin like fibers which can be needle punched and/or hydroentangled to produce a superior fabric and garments using a minimum amount of carrier fibers.
Recycled fibers also can comprise synthetic fibers, plant fibers, regenerated cellulose fibers, pulp fibers or the like. Conventional methods for mechanical recycling of fibers from nonwoven and textile material are well known.
U.S. Pat. No. 5,481,864 describes a conventional process for recycling cloth scraps to produce a yarn from the fibers contained in the cloth. The process includes moistening the cloth scraps and maintaining the moisture conditioning at a level of at least 10 per cent throughout the process. The process of maintaining fibers in a moist state throughout the shredding process has disadvantages. The web of moist fibers weighs more and the fibers tend to progressively agglutinate and clog the cutting pins of the cylinders in the tearing line. This tends to slow the process and makes the machines run hotter. The progressive agglutination of the fibers also reduces the cutting action and prevents fibers from being fully opened.
The inability to open the moisture laden fibers results in a finished nonwoven product which comprises typically weak, soft and bulky yarn. A web of material comprising such unopened fibers does not have uniform density and is not suitable for hydroentanglement, nor for the production of a strong nonwoven material which would be be capable of use for a wide variety of applications.
Conventionally, surplus fibers, particularly cotton, are opened from a bale and cleaned on air carding machines which act to separate the fibers, ideally to a single fiber state. In order to open the fibers, it is necessary to extract at least some of the surface additives such as starches, binders, or other materials which alter the surface properties of the fibers and prevent fibers from being easily opened.
Binders are typically glues or other types of adhesives which cling to fibers and make them unacceptable for reuse in applications requiring fiber sterility. Binders especially need to be removed from recycled fibers in order to enable the fibers to be opened and reused for other applications
U.S. Pat. No. 6,037,282 discloses a conventional process for making a nonwoven material by hydroentangling a fiber web. The fibers used for forming the web comprise waste synthetic fibers, plant fibers, regenerated cellulose fibers or pulp fibers. The fibers are developed by mechanically tearing or shredding a waste material into small bits by conventional methods. The fibers are then blown randomly onto screens and air laid. This creates a random orientation of fibers on a web. Such a random orientation of fibers, when applied to hydroentanglement, produces a structurally inferior product characterized by varying thread density, unopened fibers, neps and other unconformities which render the finished hydroentangled product incapable of being cross lapped or laminated, and thus limits useful applications.
A further disadvantage of the process taught by U.S. Pat. No. 6,037,282 is that the tearing action for freeing the fibers also shreds and stretches the fibers along the longitudinal axis, resulting in weakened, frayed and distorted fibers which may end up twisted and difficult to open. U.S. Pat. No. 6,037,282 concedes that the freeing of the fibers is often incomplete and the fibers clump together to form flocks. The flocks in turn produce nonuniformities in the final nonwoven product, resulting in reduced strength. (See U.S. Pat. No. 6,037,282 at col. 2, lines 54-63; xe2x80x9cnotably lower strength,xe2x80x9d col. 3, lines 58-62.)
A conventional process such as U.S. Pat. No. 6,037,282 must compensate for reduced strength of the hydroentangled product by adding binders such as polyamide-epichlorohydrin, EVA, latex, or the like. The amount of additive is between 0.1 and 10 percent by weight, preferably between 1 and 5 percent by weight, calculated as part of the weight of the material (Column 3, lines 2-4). However, this puts surface impurities onto the fibers, making them unsuitable for many applications requiring medical sterility or high absorbency. The addition of binders makes the resulting fibers, which are already weakened, even more difficult to open in the event the nonwoven product is to be recycled. Thus, the addition of binders limits the finished nonwoven material to a single use product.
In addition to adding undesirable binders, a conventional process such as in U.S. Pat. No. 6,037,282 also results in so many unopened fibers and threads that the unopened threads cannot be cleaned of trash such as surface impurities, binders, and other additives. Thus, a hydroentangled product made from such a large proportion of unopened fibers is unusable except for limited applications, such as an industrial wiping or drying material.
Therefore, what is needed is a system for reconstituting fibers from waste or surplus materials, wherein the reconstituted fibers can be applied to a hydroentangling process to produce a nonwoven product of superior strength and uniformity, thereby enabling the final product to be used in a wide variety of applications.
What is also needed is a method for opening fibers of recyclable materials and for removing trash, binders, starches, and other surface impurities from the opened fibers. Such a process advantageously would provide structurally stronger, cleaner fibers which would be more amenable to hydroentangling. A nonwoven product embodying such engineered fibers would be characterized by surface uniformity, high strength and would be suitable for a wide variety of household and industrial applications.
What is also needed is a method for recycling a tightly woven fabric such as cotton denim and for fully opening those fibers with minimal distortion and loss of structural integrity due to tearing and shredding the fibers along their longitudinal axis, such that the fibers may be reused in making a hydroentangled product without defects.
In addition, it would be highly desirable to provide a process for engineering or structurally reconstituting reclaimed fibers which would open and remove all surface additives and impurities from the fibers. Thus, a hydroentangled product comprising such fibers could be made without the need for binders and would conform to high standards of medical sterility for medical, cosmetic, and other applications requiring a contamination free product. Such a hydroentangled product, made without binders, also easily could be recycled for other applications, thereby providing a multi use, resource sustainable product.
In order to achieve the foregoing objectives and other advantages, an aspect of the invention reconstitutes fibers from recycled or waste fabrics, including cotton denim waste, and forms the reconstituted fibers into a hydroentangled product characterized by substantially uniform fiber density, greater tensile strength and preferential fiber orientation. This enables the hydroentangled material to be cross lapped or laminated with other materials for greatly increased strength. For example, hydroentangled materials comprising directionally oriented fibers in accordance with an aspect of the invention can be cross lapped and coated with a polyurethane laminate barrier, which provides an absolute barrier to blood borne pathogens and has widespread benefit in medical applications.
An aspect of the invention provides a means for granulating the fibers and for conveying fibers through a series of cutting screens, such that the fibers are cut substantially across their diameter, thereby minimizing fiber distortion and preserving the structural integrity of the fibers.
Another aspect of the invention applies steam in combination with an enzyme scrubbing process for completely opening fibers of recycled waste material including cotton denim waste. This substantially removes all surface impurities from the opened fibers including starches, adhesives, binders, and other contaminants. This enables a nonwoven product produced from such fibers to meet stringent standards of sterility for medical applications.
In accordance with another aspect of the invention, a carding/equalization process provides a web of fibers for hydroentanglement characterized by unidirectional fiber orientation and uniform fiber density. The resulting hydroentangled product is structurally different from one produced by a conventional hydroentangled fiber web, in that it is characterized by a preferential fiber orientation and can be cross lapped or laminated with other materials.
The foregoing aspects of the invention also eliminate the need for adding binders and adhesives to the recycled fibers in order to provide material strength. Thus, a nonwoven product produced in accordance with the invention is amenable to further recycling, thereby providing a sustainable, multiple use product.